0328. Odd Even Linked List (M)

Odd Even Linked List (M)

题目

Given a singly linked list, group all odd nodes together followed by the even nodes. Please note here we are talking about the node number and not the value in the nodes.

You should try to do it in place. The program should run in O(1) space complexity and O(nodes) time complexity.

Example 1:

Input: 1->2->3->4->5->NULL
Output: 1->3->5->2->4->NULL

Example 2:

Input: 2->1->3->5->6->4->7->NULL
Output: 2->3->6->7->1->5->4->NULL

Constraints:

• The relative order inside both the even and odd groups should remain as it was in the input.
• The first node is considered odd, the second node even and so on ...
• The length of the linked list is between [0, 10^4].

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题意

将给定链表的奇数结点移到前半部分，偶数结点移到后半部分。(奇偶性指结点本身而不是结点内的数)

思路

将奇偶结点拆成两个链表再合并即可。

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代码实现

Java

class Solution {
    public ListNode oddEvenList(ListNode head) {
        ListNode oddDummy = new ListNode();
        ListNode odd = oddDummy;
        ListNode evenDummy = new ListNode();
        ListNode even = evenDummy;
        boolean isOdd = true;
        while (head != null) {
            if (isOdd) {
                odd.next = head;
                odd = head;
            } else {
                even.next = head;
                even = head;
            }
            head = head.next;
            isOdd = !isOdd;
        }
        even.next = null;
        odd.next = evenDummy.next;
        return oddDummy.next;
    }
}